
Prior probability (odds): 
18% (0.2) 

POSITIVE TEST: 
Positive Likelihood ratio: 
8.70 
95% confidence interval: 
[5.65,13] 
Posterior probability (odds): 
66% (1.9) 
95% confidence interval: 
[55%,74%] 
(~ 1 in 1.5 with positive test 
are sick) 

NEGATIVE TEST: 
Negative Likelihood ratio: 
0.24 
95% confidence interval: 
[0.14,0.40] 
Posterior probability (odds): 
5% (0.1) 
95% confidence interval: 
[3%,8%] 
(~ 1 in 1.1 with negative test 
are well) 

Odds = Probability / (1Probability) 
+LR = Sensitivity / (1  Specificity) 
LR = (1  Sensitivity) / Specificity 
Posterior Odds = Prior Odds x LR 
